全文获取类型
收费全文 | 1347篇 |
免费 | 17篇 |
国内免费 | 16篇 |
专业分类
化学 | 829篇 |
晶体学 | 9篇 |
力学 | 50篇 |
数学 | 195篇 |
物理学 | 297篇 |
出版年
2022年 | 11篇 |
2021年 | 15篇 |
2020年 | 14篇 |
2017年 | 10篇 |
2016年 | 20篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 67篇 |
2012年 | 35篇 |
2011年 | 66篇 |
2010年 | 45篇 |
2009年 | 31篇 |
2008年 | 43篇 |
2007年 | 63篇 |
2006年 | 48篇 |
2005年 | 53篇 |
2004年 | 48篇 |
2003年 | 38篇 |
2002年 | 45篇 |
2001年 | 34篇 |
2000年 | 35篇 |
1999年 | 36篇 |
1998年 | 12篇 |
1997年 | 20篇 |
1996年 | 32篇 |
1995年 | 20篇 |
1994年 | 18篇 |
1993年 | 32篇 |
1992年 | 12篇 |
1991年 | 21篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 29篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 18篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 14篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1972年 | 12篇 |
1968年 | 9篇 |
排序方式: 共有1380条查询结果,搜索用时 15 毫秒
41.
Stuart M. Marshall Douglas G. Moore Alastair R. G. Murray Sara I. Walker Leroy Cronin 《Entropy (Basel, Switzerland)》2022,24(7)
Assembly theory (referred to in prior works as pathway assembly) has been developed to explore the extrinsic information required to distinguish a given object from a random ensemble. In prior work, we explored the key concepts relating to deconstructing an object into its irreducible parts and then evaluating the minimum number of steps required to rebuild it, allowing for the reuse of constructed sub-objects. We have also explored the application of this approach to molecules, as molecular assembly, and how molecular assembly can be inferred experimentally and used for life detection. In this article, we formalise the core assembly concepts mathematically in terms of assembly spaces and related concepts and determine bounds on the assembly index. We explore examples of constructing assembly spaces for mathematical and physical objects and propose that objects with a high assembly index can be uniquely identified as those that must have been produced using directed biological or technological processes rather than purely random processes, thereby defining a new scale of aliveness. We think this approach is needed to help identify the new physical and chemical laws needed to understand what life is, by quantifying what life does. 相似文献
42.
V. Aranda J. M. Christensen M. U. Alzueta P. Glarborg S. Gersen Y. Gao P. Marshall 《国际化学动力学杂志》2013,45(5):283-294
A detailed chemical kinetic model for oxidation of CH3OH at high pressure and intermediate temperatures has been developed and validated experimentally. Ab initio calculations and Rice–Ramsperger–Kassel–Marcus/transition state theory (RRKM/TST) analysis were used to obtain rate coefficients for , , , and . The experiments, involving CH3OH/O2 mixtures diluted in N2, were carried out in a high‐pressure flow reactor at 600–900 K and 20–100 bar, varying the reaction stoichiometry from very lean to fuel‐rich conditions. Under the conditions studied, the onset temperature for methanol oxidation was not dependent on the stoichiometry, whereas increasing pressure shifted the ignition temperature toward lower values. Model predictions of the present experimental results, as well as rapid compression machine data from the literature, were generally satisfactory. The governing reaction pathways have been outlined based on calculations with the kinetic model. Unlike what has been observed for unsaturated hydrocarbons, the oxidation pathways for CH3OH under the investigated conditions were very similar to those prevailing at higher temperatures and lower pressures. At the high pressures, the modeling predictions for onset of reaction were particularly sensitive to the reaction. 相似文献
43.
Zixin Huang Josie E. Auckett Peter E. R. Blanchard Brendan J. Kennedy Wojciech Miiller Qingdi Zhou Maxim Avdeev Mark R. Johnson Mohamed Zbiri Gaston Garbarino William G. Marshall Qinfen Gu Chris D. Ling 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(13):3482-3485
Pressure‐induced charge transfer from Bi to Ir/Ru is observed in the hexagonal perovskites Ba3+nBiM2+nO9+3n (n=0,1; M=Ir,Ru). These compounds show first‐order, circa 1 % volume contractions at room temperature above 5 GPa, which are due to the large reduction in the effective ionic radius of Bi when the 6s shell is emptied on oxidation, compared to the relatively negligible effect of reduction on the radii of Ir or Ru. They are the first such transitions involving 4d and 5d compounds, and they double the total number of cases known. Ab initio calculations suggest that magnetic interactions through very short (ca. 2.6 Å) M M bonds contribute to the finely balanced nature of their electronic states. 相似文献
44.
Stacey N. Anderson Mark Noble Katarzyna Grubel Brooks Marshall Atta M. Arif 《Journal of Coordination Chemistry》2014,67(23-24):4061-4075
The visible light-induced CO-release reactivity of the zinc flavonolato complex [(6-Ph2TPA)Zn(3-Hfl)]ClO4 (1) has been investigated in 1?:?1 H2O?:?DMSO. Additionally, the effect of ligand secondary microenvironment on the aqueous stability and visible light-induced CO-release reactivity of zinc flavonolato species has been evaluated through the preparation, characterization, and examination of the photochemistry of compounds supported by chelate ligands with differing secondary appendages, [(TPA)Zn(3-Hfl)]ClO4 (3; TPA = tris-2-(pyridylmethyl)amine) and [(bnpapa)Zn(3-Hfl)]ClO4 (4; bnpapa = N,N-bis((6-neopentylamino-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine)). Compound 3 undergoes reaction in 1?:?1 H2O?:?DMSO resulting in the release of the free neutral flavonol. Irradiation of acetonitrile solutions of 3 and 4 at 419 nm under aerobic conditions results in quantitative, photoinduced CO-release. However, the reaction quantum yields under these conditions are lower than that exhibited by 1, with 4 exhibiting an especially low quantum yield. Overall, the results of this study indicate that positioning a zinc flavonolato moiety within a hydrophobic microenvironment is an important design strategy toward further developing such compounds as CO-release agents for use in biological systems. 相似文献
45.
Transient spectroscopic characterization of the ring‐opening reaction of tetrahydrochromeno[2,3‐dimethyl]indole 下载免费PDF全文
Ariel S. Marshall Robert A. Rogers Joseph W. Perry W. J. Brittain 《Journal of Physical Organic Chemistry》2016,29(5):221-226
Tetrahydrochromeno is a structural variant of spiropyran that undergoes a reversible ring‐opening to generate a colored nitrophenolate intermediate. Earlier work confirmed this intermediate through trimethylsilyl cyanide trapping under continuous irradiation. We have performed transient absorption spectroscopy to further characterize the mechanism of the ring‐opening reaction. Excitation at 355 nm produced a transient species with an absorption maximum at 445 nm, which we assign to the nitrophenolate unit of the ring‐opened product. The transient absorption decays after ~970 ns with small optical density changes corresponding to a 0.15 quantum yield. Exposure to oxygen did not exhibit a significant deleterious effect on the photoisomerization of the chromeno dye. Time‐dependent density functional theory corroborated spectroscopic assignments of the starting chromeno and the putative ring‐opened intermediate. The excited state behavior of this system parallels the structurally similar oxazine system reported by Raymo and coworkers. The one significant difference is the longer lifetime of the photochemically generated intermediate from chromeno. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
46.
Dr. Alif Sussardi Dr. Ross J. Marshall Prof. Stephen A. Moggach Prof. Anita C. Jones Prof. Ross S. Forgan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(60):14871-14875
Photophysical studies of chromophoric linkers in metal–organic frameworks (MOFs) are undertaken commonly in the context of sensing applications, in search of readily observable changes of optical properties in response to external stimuli. The advantages of the MOF construct as a platform for investigating fundamental photophysical behaviour have been somewhat overlooked. The linker framework offers a unique environment in which the chromophore is geometrically constrained and its structure can be determined crystallographically, but it exists in spatial isolation, unperturbed by inter-chromophore interactions. Furthermore, high-pressure studies enable the photophysical consequences of controlled, incremental changes in local environment or conformation to be observed and correlated with structural data. This approach is demonstrated in the present study of the trans-azobenzene chromophore, constrained in the form of the 4,4’-azobenzenedicarboxylate (abdc) linker, in a UiO topology framework. Previously unobserved effects of pressure-induced solvation and conformational distortion on the lowest energy, nπ* transition are reported, and interpreted the light of crystallographic data. It was found that trans-azobenzene remains non-fluorescent (with a quantum yield less than 10−4) despite the prevention of trans-cis isomerization by the constraining MOF structure. We propose that efficient non-radiative decay is mediated by the local, pedal-like twisting of the azo group that is evident as dynamic disorder in the crystal structure. 相似文献
47.
Scott B. Ficarro Jessica M. Biagi Jinhua Wang Jenna Scotcher Rositsa I. Koleva Joseph D. Card Guillaume Adelmant Huan He Manor Askenazi Alan G. Marshall Nicolas L. Young Nathanael S. Gray Jarrod A. Marto 《Journal of the American Society for Mass Spectrometry》2014,25(4):636-650
We assemble a versatile molecular scaffold from simple building blocks to create binary and multiplexed stable isotope reagents for quantitative mass spectrometry. Termed Protected Amine Labels (PAL), these reagents offer multiple analytical figures of merit including, (1) robust targeting of peptide N-termini and lysyl side chains, (2) optimal mass spectrometry ionization efficiency through regeneration of primary amines on labeled peptides, (3) an amino acid-based mass tag that incorporates heavy isotopes of carbon, nitrogen, and oxygen to ensure matched physicochemical and MS/MS fragmentation behavior among labeled peptides, and (4) a molecularly efficient architecture, in which the majority of hetero-atom centers can be used to synthesize a variety of nominal mass and sub-Da isotopologue stable isotope reagents. We demonstrate the performance of these reagents in well-established strategies whereby up to four channels of peptide isotopomers, each separated by 4 Da, are quantified in MS-level scans with accuracies comparable to current commercial reagents. In addition, we utilize the PAL scaffold to create isotopologue reagents in which labeled peptide analogs differ in mass based on the binding energy in carbon and nitrogen nuclei, thereby allowing quantification based on MS or MS/MS spectra. We demonstrate accurate quantification for reagents that support 6-plex labeling and propose extension of this scheme to 9-channels based on a similar PAL scaffold. Finally, we provide exemplar data that extend the application of isotopologe-based quantification reagents to medium resolution, quadrupole time-of-flight mass spectrometers. Figure
115F 相似文献
48.
Lutz Schweikhard Alan G. Marshall 《Journal of the American Society for Mass Spectrometry》1993,4(6):433-452
Various geometric configurations for the excitation of coherent ion motion in Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR/MS) are analyzed (in some cases for the first time) with unified notation. The instantaneous power absorption, F v, in which v is ion velocity and F the force produced by the applied excitation electric field (harmonic, single frequency, on-resonance, in-phase), is time averaged and then set equal to the time rate of change of ion total (cyclotron + magnetron + trapping) energy, to yield a differential equation that is readily solved for the (time-dependent) amplitude of each of the various ion motions. The standard FT-ICR excitation (namely, radial dipolar) is reviewed. The effects of quadrature and radial quadrupolar excitation on ion radial (cyclotron and magnetron) motions are also reviewed. Frictional damping is shown to decrease the ion cyclotron orbital radius and trapping amplitude but increase the magnetron radius. Feedback excitation (i.e., excitation at the simultaneously detected ion cyclotron orbital frequency of the same ion packet) is introduced and analyzed as a means for exciting ions whose cyclotron frequency changes during excitation (as for relativistically shifted low-mass ions). In contrast to conventional radial dipolar excitation, axial dipolar excitation of the trapping motion leads to a mass-dependent ion motional amplitude. Parametric (i.e., axial quadrupolar) excitation is shown to produce an exponential increase in the ion motional amplitudes (hyperbolic sine and hyperbolic cosine amplitude for cyclotron and magnetron radii, respectively). More detailed consideration of parametric excitation leads to an optimal ion initial radial position in parametric-mode FT-ICRjMS. 相似文献
49.
Anthony Marshall Martin Tkaczyk Alex G. Harrison 《Journal of the American Society for Mass Spectrometry》1991,2(4):292-298
The negative ion chemical ionization mass spectra of twentyeight C4 to C7 carbonyl compounds were recorded using the oxide radical anion O?? as reagent ion. As noted earlier, the reactions occurring include H+ abstraction, H 2 +? abstraction, H? atom displacement, and alkyl radical displacement. In addition, the [M?2H]? ions fragment further by alkyl radical elimination. The relative importance of these reactions depends strongly on molecular structure, with the result that isomer distinction frequently is possible. Where this is not possible, as for isomeric aldehydes, the collisional charge inversion mass spectra of common product ions provides isomer distinction. The H 2 +? abstraction reaction is shown to involve abstraction not only of two hydrogens from the same α-carbon but also, in part, abstraction of one hydrogen from each α-carbon. 相似文献
50.
Kleckner D Marshall W de Dood MJ Dinyari KN Pors BJ Irvine WT Bouwmeester D 《Physical review letters》2006,96(17):173901
We report on the demonstration of a high finesse micro-optomechanical system and identify potential applications ranging from optical cooling to weak force detection to massive quantum superpositions. The system consists of a high quality diameter flat dielectric mirror cut from a larger substrate with a focused ion beam and attached to an atomic force microscope cantilever. Cavity ring-down measurements performed on a 25 mm long Fabry-Pérot cavity with the 30 microm mirror at one end show an optical finesse of 2100. Numerical calculations show that the finesse is not diffraction limited and that orders of magnitude higher finesse should be possible. A mechanical quality factor of more than 10(5) at pressures below 10(-3) mbar is demonstrated for the cantilever with a mirror attached. 相似文献